In an internal combustion engine such as a diesel engine, nitrogen oxides, particulate matter (PM), and the like are generated because of combustion. In a vehicle in which an internal combustion engine is used for power, in order to suppress discharging of these materials with exhaust gas, an oxidation catalyst (DOC) and a purifying apparatus such as a diesel particulate filter (DPF) are provided in an exhaust passage.
The DPF is an apparatus for collecting PM contained in exhaust gas by using a filter. While the DPF is used, PM is accumulated, and thus functions thereof deteriorate due to clogging of the filter. Therefore, the accumulated PM is combusted by feeding high temperature exhaust gas to the DPF. As a method for generating high temperature exhaust gas, a method of using heat which is generated by allowing unburnt hydrocarbons (HC) to be included in the exhaust gas, adsorbing the HC on a DOC provided on an upstream side, and oxidizing (combusting) the HC is generally used.
However, when the DOC exceeds a usable temperature, the DOC is likely to be degraded, and functions thereof deteriorate. Therefore, when HC is adsorbed and accumulated in the DOC more than necessary, the DOC exceeds the usable temperature at the time of combustion, and thus there is a possibility that the DOC is degraded.
Here, in the exhaust purification apparatus of Patent Literature 1, a passage for guiding exhaust gas to an adsorbent and a passage which does not pass through the adsorbent are provided, and when an estimated value of an amount of accumulated HC in the adsorbent reaches a predetermined value or more, high temperature exhaust gas is guided to the adsorbent by opening the former passage so that the accumulated HC is combusted.
In addition, in a HC adsorbing catalyst of Patent Literature 2, if the amount of accumulated HC which is estimated reaches a predetermined amount, an after-ejection (ejection in expansion cycle) is performed using an injector, a temperature of the exhaust gas is increased, and HC is burnt. In order to estimate the amount of the accumulated HC, there is a method of calculating the amount based on a change of HC concentration between ahead of and behind the HC adsorbing catalyst (former), or a method of estimating an amount of flow of HC to the HC adsorbing catalyst from a measured value of an air fuel ratio sensor and calculating the amount using the estimated amount of flow of HC, an adsorption efficiency of the HC adsorbing catalyst, and an amount of HC-oxidation/desorption of the HC adsorbing catalyst (latter).